The invention is related to a rolling element bearing, comprising an outer ring and an inner ring which enclose a bearing space containing rolling elements, the rings being comprised of steel. Normally, the rolling elements of such bearing are comprised of steel as well, in particular of steel with about the same hardness properties as the steel of the rings.
During rotation of the bearing, the rolling elements roll over the raceways of the rings. Any contaminations, for instance small wear particles, which are on the raceways or the rolling elements, become compressed between these elements. Hard wear particles, for instance small steel particles which have come off of one of the components of the bearing or have entered from the outside, resist such compression and lead to the formation of minute indentations in both the raceways and the rolling elements.
It has been found that in particular the indentations in the raceways have a negative influence on the useful bearing life. Also, they lead to increased noise during running due to unsmooth running and increased play, caused by wear of the raceway surfaces.
These indentations have a craterlike shape, whereby a small central hole is surrounded by a ridge of material that has been pushed upwardly and projects above the raceway. Conversely, the rolling elements are indented as well. Due to the cyclic character of the load exerted by the rolling elements, crack formation and fatigue may occur in the rings at the location of high stress concentrations usually located just under the ridge of an indentation.
Although it has already been proposed to protect the bearings against such detrimental contamination particles by providing seals and filters, nevertheless the ingress thereof cannot always be totally prevented and therefore the formation of indentations cannot be prevented.